The analysis will concentrate on the structural failure of the right wing spar. Weather and the pilot's medical condition were not considered to be factors in the occurrence.2.0 Analysis The analysis will concentrate on the structural failure of the right wing spar. Weather and the pilot's medical condition were not considered to be factors in the occurrence. 2.1 Spar Failure The compression damage found in the spar could have occurred either before the wood was processed for aircraft use or, later, while the spar was installed on the aircraft. Since the spar appears to have been original equipment on an aircraft manufactured in 1948, and it would be considered unusual for damage prior to fabrication to take 46 years to fail, it appears more probable that the spar failure was the result of the recent damage to the aircraft. Of the two occurrences involving damage which were documented in the aircraft logs, the event in 1985 had the most potential to cause compression damage to the right rear spar. The repair description indicates a probable loss of control resulting in a ground loop or landing gear collapse. Since the repair facility involved has gone out of business, it was not possible to determine what had occurred. Normal load reversals on the spar while in service, which would include flight loads, landing loads, and loads experienced while tied down, would result in a progressive failure at the compression damaged area. When the aircraft was on its back during the second occurrence, the spar would have been subjected to unusual bending loads that may have exacerbated the progressive nature of the fracture. The low pass and pull up conducted by the pilot finally stressed the weakened right rear spar to its limit, and it failed. The sudden loss of lift on the right wing would have resulted in the aircraft entering an uncommanded right roll from which recovery would not likely have been possible. 2.2 Inspection The aircraft had been inspected for damage following the two occurrences found in the logs and annually during the normal 100-hour inspection, but the compression damage to the spar was not detected. In order to properly inspect the spar, it would be necessary to either install additional wing inspection panels or remove the fabric cover. TC AMA 571.101/5 is deficient because it does not contain guidance for inspection requirements to detect compression failures in wooden spars. 3.0 Conclusions 3.1 Findings The pilot was certified and qualified for the flight in accordance with existing regulations. The aircraft entered an uncommanded right roll and descended vertically into the ground. The right rear wooden wing spar failed in flight due to compression damage which may have been the result of previous damage to the aircraft. The wing spar damage was not detected during initial repair or subsequent annual inspections. The pilot/owner had not selected or identified an inspection program in the journey log as required by regulation. The inspection form used by the maintenance facility during the last annual inspection did not include visual inspection of the wing spar for condition as required by AWM, Chapter 571. The inspection panels installed on the wing would not allow for adequate examination of the spars for damage. The aircraft was equipped with obsolete fabric-to-metal type seat-belts. Mogas fuel was being used without the STC approval required by regulation. The aircraft was not equipped with an ELT. AMA 571.101/5 does not contain guidelines on how to detect compression damage in wooden spars. 3.2 Causes The wing failure may have been the result of a previous occurrence involving damage to the right wing that was inadequately inspected both at the time of repair and during subsequent annual inspections. The Board has no aviation safety recommendations to issue at this time.4.0 Safety Action The Board has no aviation safety recommendations to issue at this time.